1. Field of the Invention
The present invention relates to an information processing unit, an information processing method, and a program. More particularly, the invention relates to an information processing unit, an information processing method, and a program ideally used in a case where a slot for mounting a variety of devices, such as a storage device, is provided in a control board.
2. Description of the Related Art
In a personal computer to which a universal serial bus (USB) device can be connected, a connection port for the USB device is connected to a USB host controller. If the USB device is connected to the connection port for the USB device, i.e., if a USB connector is connected, then the USB host controller sends, for example, 3,000 to 4,000 (depending upon each personal computer) interrupts per second to a central processing unit (CPU).
A small personal computer drivable by batteries is required to consume less power in order to enable a user to carry it and use it as long as possible at a desired place. To meet such a demand, according to the art disclosed in Japanese Unexamined Patent Application Publication No. 2000-10907, if no USB device is connected to a USB port, that is, if no connector is connected, then the function of the USB host controller is suspended. The art makes it possible to restrain wasteful power consumption by the USB host controller so as to prolong the operating time in a battery-driven mode.
In a personal computer, if, for example, a slot or other USB device for mounting a storage device or the like is connected to a USB host controller and provided on a control board beforehand, then the USB device cannot be detached, so that it is always in connection with the USB host controller. This means that the USB host controller constantly detects the USB device on the board regardless whether the USB device is in operation, and therefore sends, for example, 3,000 to 4,000 interrupts per second to a CPU.
The CPU has a plurality of operation modes to control power consumption. For instance, PENTIUM II (registered trademark) or PENTIUM III (registered trademark) has four operation modes, C0, C1, C2, and C3. In the operation mode C0, the CPU operates at full speed. C1 denotes a mode called “AutoHALT,” C2 denotes a mode called “QuickStart,” and C3 denotes a mode called “DeepSleep.” The power is consumed less in C2 than C1, and less in C3 than C2. For the CPU to be set to the C3 mode, the frequency of interrupts sent to the CPU must be, for example, less than about 200 per second, although it depends on the type of CPU and the types of its peripheral devices.
Hence, if a USB device is provided on a control board, then CPU cannot change its setting to a low power consumption mode (e.g., the C3 status).